Konrad Schindler

3D MURALE: a multimedia system for archaeology

This paper introduces the 3D Measurement and Virtual Reconstruction of Ancient Lost Worlds of Europe system (3D MURALE). It consists of a set of tools for recording, reconstructing, encoding, visualising and database searching/querying that operate on buildings, building parts, statues, statue parts, pottery, stratigraphy, terrain geometry and texture and material texture. The tools are loosely linked together by a common database on which they all have the facility to store and access data. The paper describes the overall architecture of the 3D MURALE system and then briefly describes the functionality of the tools provided by the project. The paper compares the multimedia studio architecture adopted in this project with other multimedia studio architectures.

A model-based method for building reconstruction

Model-based reconstruction methods are applied to the detailed reconstruction of buildings from close-range images. The 3D points obtained through image matching are segmented into a coarse polyhedral model with a robust regression algorithm, then the geometry of this model is refined with predefined shape templates in order to automatically recover a CAD-like model of the building surface. Reprojection of the 3D shape templates is used to optimally fit their parameters to the image information. Throughout the paper the investigated methods are demonstrated on real datasets.

Piecewise planar scene reconstruction from sparse correspondences

A novel method able to recover scene planes of arbitrary position and orientation from oriented images using homographies is presented. Planar regions are reconstructed using only sparse, affine-invariant sets of corresponding seed regions. These regions are iteratively expanded and refined using plane-induced homographies. Experiments on synthetic data show the high accuracy of the reconstruction and demonstrate that the reconstruction method can cope with large baseline changes. Experiments on real images show the performance of the method on practically relevant scenes.

A work-flow and data model for reconstruction, management, and visualization of archaeological sites

We propose a framework for a complex visualization environment suitable for archaelogical applications. Given 2D and 3D data derived from appropriate acquisition processes, the scene is organized in a structure that can easily be incorporated into a database. Special care is taken on attributes such as time and likelihood of scientific hypothesises which are important for a correct interpretation of the excavation site. After a preprocessing step, the database content can directly be used to visualize the scene in a standalone virtual reality installation in a museum as well as on the internet.

On Robust Regression in Photogrammetric Point Clouds

Many applications in computer vision require robust linear regression on photogrammetrically reconstructed point clouds. Due to the modeling process from perspective images the uncertainty of an object point depends heavily on its location in object space w.r.t. the cameras. Standard algorithms for robust regression are based on distance measures from the regression surface to the points, but these distances are biased by varying uncertainties. In this paper a description of the local object point precision is given and the Mahalanobis distance to a plane is derived to allow unbiased regression. Illustrative examples are presented to demonstrate the effect of the statistically motivated distance measure.

Generalized use of homographies for piecewise planar reconstruction

We present a method for piecewise planar modeling from oriented images. The method uses a set of homologous image points and the underlying 3D geometry to determine image regions which satisfy plane-induced homographies. It robustly detects and reconstructs planes of arbitrary position and orientation in the scene and takes advantage of the regular raster structure of the images to delineate the regions.

Providing multimedia tools for recording, reconstruction, visualisation and database storage/access of archaeological excavations

Over the years archaeologists have been swift to embrace new advances in technology that allow them to more comprehensively document the results of their work. Today it is commonplace to find information technologies, in the form MS Office-type tools with some CAD and GIS, deployed for primary data capture, analysis, presentation and publication. While these computing technologies can be used effectively to record and interpret archaeological sites, the radical developments in 3D recording, reconstruction and visualisation tools have had relatively limited impact upon the archaeological community. This is unfortunate as these new technologies have the potential to (a) enable the archaeologists to record their unrepeatable experiments to unprecedented levels of accuracy, (b) enable the archaeologists to reconstruct artefacts such as pottery from sherds, textures and sites from different eras (c) visualise the wealth of excavated information in dynamic new ways away from the archaeological site during post-excavation analysis, (d) make this wealth of detail available to the scholarly community as part of the publication process and secure its digital longevity through its deposition in a trusted digital library/archive and (e) communicate the excitement and importance of their archaeological site and its finds to an interested non-academic audience. This paper describes the overall concept of the EU funded project, 3D Measurement and Virtual Reconstruction of Ancient Lost Worlds of Europe (3D MURALE), that has developed and created a set of low-cost multimedia tools for recording, reconstructing, encoding, and visualising archaeological artefacts and site.

Spatial subdivision for piecewise planar object reconstruction

An algorithm is presented for piecewise planar segmentation of 3D point clouds, which uses spatial subdivision into finite volume elements. For each volume element a local plane is fitted and these planes are grouped to detect bigger planar structures and construct a piecewise planar object model. The algorithm has a higher detection sensitivity for small object planes than a previous global plane detection methods based on RANSAC fitting and plane sweeping. Experimental results are presented for a synthetic dataset, which was used to evaluate the algorithms performance and for a real dataset, which was used to compare it to other methods.

The epipolar geometry of the log-polar image plane

This work presents an explicit formulation of the epipolar geometry of two oriented log-polar images. A method is derived for efficient pixel-by-pixel computation of epipolar lines in the log-polar plane, which are complicated nonlinear functions. As an example, the method is applied for dense stereo matching: it is shown that it is more efficient to perform one-dimensional disparity estimation in the log-polar plane than to remap the images to Cartesian coordinates.

Web-based visualization of virtual archaeological sites

We present a web-based visualization tool for archaeological sites that has been developed within the 3D Murale project. The problem of structuring the scene prior to visualization is addressed by an extension to the 3D modeling and animation package MayaTM which enables communication with the common data pool of 3D Murale. Texture data is prepared for visualization by encoding it using the JPEG 2000 standard, which is based on wavelet technology and allows easy access to encoded images at different resolutions. Finally, we provide an ActiveX plugin for the Microsoft Internet Explorer to enable convenient exploration of the archaeological scene in a web environment. n nOur approaches are demonstrated using a model of a frieze of dancing girls (Sagalassos, southwest Turkey). The discussion of our methods is supported by performance data and screen shots.